Methamphetamine is a drug of abuse and in high doses causes toxicity to dopaminergic terminals in striatum as well as other neural components. The mechanism associated with this toxicity is not known although oxidative stress, dopamine, and hyperthermia have been hypothesized to play a role in the toxic outcome. Several studies have suggested that mitochondrial dysfunction may play a role in the mechanism of methamphetamine-induced neurotoxicity, but this has not been examined directly. Therefore, in this application, we propose to examine the hypothesis that mitochondrial dysfunction resulting from exposure to high doses of methamphetamine is a critical step in the resulting neurotoxicity. We will focus on the fundamental question of whether exposure to methamphetamine causes mitochondrial dysfunction by direct effects of methamphetamine, indirect effects such as increases in cytoplasmic dopamine, or a combination of both, resulting in DA terminal damage or cell death. We propose to examine this in a variety of in vitro and in vivo models taking advantage of the unique characteristics of each system. In increasingly complex systems, we will examine mitochondrial function and cell viability following acute and chronic exposure to methamphetamine in (1) isolated mitochondria and synaptosomes, (2) cell cultures, (3) cortico-striatal-mesenephalic organotypic cultures, and (4) the in vivo rat model. In the rat model, in addition to the functional analyses of mitochondria, we will also examine mitochondrial protein modifications and potential therapeutic approaches to enhance mitochondrial function and limit toxicity. We know that individuals who abuse amphetamines, even the occasional binge abuser, are at increased risk for the development of permanent damage to the CNS. This may also predispose them later in life to neurological disorders such as Parkinson's disease. The ultimate goal of this study will be to identify new targets and approaches for therapeutic intervention to prevent methamphetamine-induced neurotoxicity.